/0 Subnet
The entire IPv4 internet
A /0 covers every IPv4 address in existence. Used exclusively as the default route (0.0.0.0/0) — the "catch-all" in routing tables and firewall rules.
Common Use Cases
- → Default route / route of last resort
- → Firewall "allow all" or "deny all" rule
- → BGP full routing table advertisement
Example /0 Networks
| CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|
| 0.0.0.0/0 | 0.0.0.0 | 0.0.0.1 | 255.255.255.254 | 255.255.255.255 | 4,294,967,294 |
| 0.0.0.0/0 | 0.0.0.0 | 0.0.0.1 | 255.255.255.254 | 255.255.255.255 | 4,294,967,294 |
| 0.0.0.0/0 | 0.0.0.0 | 0.0.0.1 | 255.255.255.254 | 255.255.255.255 | 4,294,967,294 |
| 0.0.0.0/0 | 0.0.0.0 | 0.0.0.1 | 255.255.255.254 | 255.255.255.255 | 4,294,967,294 |
| 0.0.0.0/0 | 0.0.0.0 | 0.0.0.1 | 255.255.255.254 | 255.255.255.255 | 4,294,967,294 |
| 0.0.0.0/0 | 0.0.0.0 | 0.0.0.1 | 255.255.255.254 | 255.255.255.255 | 4,294,967,294 |
How /0 Compares
Frequently Asked Questions
How many IPs are in a /0?
A /0 subnet contains 4,294,967,296 total IP addresses and 4,294,967,294 usable host addresses. The network address (first IP) and broadcast address (last IP) are reserved and cannot be assigned to hosts.
What is the subnet mask for /0?
The subnet mask for a /0 is 0.0.0.0.
In CIDR notation, the prefix length /0 means
the first 0 bits of the address are the network portion.
The wildcard (inverse) mask is 255.255.255.255.